grpc: implement WithInsecure() using the insecure package (#4718)

dialoptions.go

@@ -27,6 +27,7 @@ import (
 	"google.golang.org/grpc/backoff"
 	"google.golang.org/grpc/balancer"
 	"google.golang.org/grpc/credentials"
+	"google.golang.org/grpc/credentials/insecure"
 	"google.golang.org/grpc/internal"
 	internalbackoff "google.golang.org/grpc/internal/backoff"
 	"google.golang.org/grpc/internal/transport"
@@ -49,7 +50,6 @@ type dialOptions struct {
 	bs              internalbackoff.Strategy
 	block           bool
 	returnLastError bool
-	insecure        bool
 	timeout         time.Duration
 	scChan          <-chan ServiceConfig
 	authority       string
@@ -298,11 +298,17 @@ func WithReturnConnectionError() DialOption {
 }
 
 // WithInsecure returns a DialOption which disables transport security for this
-// ClientConn. Note that transport security is required unless WithInsecure is
-// set.
+// ClientConn. Under the hood, it uses insecure.NewCredentials().
+//
+// Note that using this DialOption with per-RPC credentials (through
+// WithCredentialsBundle or WithPerRPCCredentials) which require transport
+// security is incompatible and will cause grpc.Dial() to fail.
+//
+// Deprecated: use insecure.NewCredentials() instead.
+// Will be supported throughout 1.x.
 func WithInsecure() DialOption {
 	return newFuncDialOption(func(o *dialOptions) {
-		o.insecure = true
+		o.copts.TransportCredentials = insecure.NewCredentials()
 	})
 }